


And the Charged Atmosphere

by flickerface



Category: Ghostbusters (2016), The Librarians (TV 2014)
Genre: Dubious Science, F/F, Romance, Some Plot, actually a fair amount of plot, missing episode
Language: English
Status: Completed
Published: 2016-08-19
Updated: 2016-08-19
Packaged: 2018-08-09 19:02:47
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 7
Words: 9,173
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7813519
Author URL: https://archiveofourown.org/users/flickerface/pseuds/flickerface
Summary: <blockquote class="userstuff">
              <p>It's been six months since the team of Librarians reached Manhattan just in time to see a vortex reverse itself, ghosts get sucked in, and a historic skyscraper re-construct itself. (The noise Stone made was painful. Jenkins just tsk'd.) But while the...Ghostbusters...closed the vortex, the power that had been pushed into the ley lines was very much still present. The Ghostbusters didn't seem to notice.</p><p>The Librarians definitely had.</p>
            </blockquote>





	1. Chapter 1

**Author's Note:**

  * For [seatides](https://archiveofourown.org/users/seatides/gifts).



> For seatides, who whispered "HOLTZMANN AND CASSANDRA" very intensely into my ear before the movie was even over. <3

Cassandra's clippings book shakes in her pocket at 10:32 PM while she's writing an equation on one of the chalkboard walls in the room she's claimed for her own.

Five minutes later, she skids into the Annex reading room. "Mine! This one's all mine!" Nobody's there, but the door is set to go to Portland—the one in Maine—so she's safe. Cassie pulls the globe around to New York City, fiddles the coordinates until they're just right, and yanks the doors open.

A dark library awaits her, its shelves stretching off into darkness where the light from the Library doesn't quite fall.

Cassie grabs a flashlight and steps through.

It's been six months since the team of Librarians reached Manhattan just in time to see a vortex reverse itself, ghosts get sucked in, and a historic skyscraper re-construct itself. (The noise Stone made was painful. Jenkins just tsk'd.) But while the...Ghostbusters...closed the vortex, the power that had been pushed into the ley lines was very much still present. The Ghostbusters didn't seem to notice.

The Librarians definitely had. The uptick in strange occurrences in New York City had been considerable, which was saying something for New York City. Most of the activity wasn't ghosts; most of it wasn't benevolent, either. They had had their hands full since then, banishing evil sorcerers who sucked the life-energy from people through Broadway performances and chasing off trolls who tried to eat the subway trains. It was a good thing Flynn had gotten used to there being more than one Librarian, because one Librarian would've collapsed under the workload in a week.

The Library's doors close behind Cassie, becoming an innocuous service entrance. She switches her flashlight on, pointing it at the nearest shelves. Literature: okay, she's in the wrong section. She follows the rows of shelving out to the lobby.

Where someone's trying to pick the lock on one of the doors. The streetlights catch on coveralls, goggles pushed up on the person's head, a tangle of equipment— _oh, no_ , Cassie thinks. She purses her lips and, despite a strong urge to flee upstairs, walks over and pushes the neighboring door open.

The Ghostbuster, kneeling to fiddle with the lock, slews her head up to look at Cassie. She's got a ridiculous pompadour of blonde hair—how does she even keep that up, with the goggles there?—and a disarming smile.

"Are you the librarian?"

Cassie puts her forefingers together carefully. "I'm _a_ Librarian," she says, because Stone and Ezekiel will never let her hear the end of it if she claims primacy. Flynn, too, but he'd just look wounded.

"Great." She jumps to her feet, slinging her gear on and grabbing a pair of thick black rubber gauntlets from her belt. She slaps the gloves into her palm, startling Cassie. "Show me to the ghosts." Her grin is wide.

The door clicks locked behind them as Cassie leads the way up the stairs. She's never been to the Brooklyn Public Library before, but she looked at the maps ahead of time—plus, the geometry is so simple, it's whirring in her head right now, she could follow it like a beacon. _And probably run right into a wall and convince this Ghostbuster that you're crazy_ , she tells herself, focusing firmly on the physical world. Not that she isn't. But.

The next appearance of the phenomena should be in just over half an hour at the back of the science section, so that's where Cassie heads.

"Here," she says finally. Her flashlight illuminates the books, each one holding nuggets of information that Cassie yearns to know. "The ghost will appear next—here."

"Thank you very much," the Ghostbuster says. She pulls her goggles down. "There may be some slight protonic discharge and—um—ectoplasm. Not to mention radiation. But the books will be fine, don't worry about the books." She slaps Cassie's shoulder like she's being reassuring. "All right? You can just run along home now, that's good, I'll get rid of the ghosties and it'll be all better."

Cassie pulls herself up to her full height—satisfyingly, she's taller than this Ghostbuster—and says, "Excuse me?"

"You're the librarian, okay, you showed me where the problem is, great, I fix it, it goes away." She pauses, cants her head to one side. Her goggles reflect the shine of Cassie's flashlight. "Unless you're worried about maybe the ghosts have a legitimate grievance? Because Patty's much better at that sort of thing."

"No!" Cassie practically shouts. "I am not employed by the Brooklyn Public Library!" Her hands are fists at her sides.

The Ghostbuster slowly pushes her goggles back to the top of her head. She takes a different pair of glasses out of her coverall pocket—these glasses are also yellow-tinted, Cassie notes with confusion—and slides them on. She frowns at Cassie through these new glasses, leaning closer than Cassie is entirely comfortable with to inspect her face in what appears to be considerable detail.

Then she leans back. "Okaaaaay," she says. "So how do you know where the ghosts are?" Apparently reconsidering everything, she digs a device out of her other pocket and holds it up. "If we _are_ where the ghosts are..." She holds it up like she's trying to get cell phone service. The long pink wires on the top waver a little.

Cassie takes in an extremely angry breath and deliberately lets it out. "We're where the ghosts are going to be," she corrects this insolent Ghostbuster. "In twenty-eight minutes and thirty...two seconds." The hundredths of seconds are whizzing past too quickly for her to specify further. Not that the Ghostbuster has earned that kind of precision, anyway.

"Twenty-eight minutes and—" The Ghostbuster stops waving her device around and turns back to Cassie. "Thirty-two seconds? Exactly?" She uses two fingers to pull her glasses down her nose and stare at Cassie over them.

Cassie stares back. "Do you even need those to see?" she asks waspishly.

The Ghostbuster gives a crack of laughter. "Hi," she says, smiling warmly right at Cassie. "Let's start again. I'm Holtzmann." She holds her hand out. "I work with a team of scientists—and a historian—to rid our fair city of spectral beings."

Cassie shakes her hand a little nervously. "Cassie," she says. "Cassandra. I do mathemagic with a team of Librarians who try to restrain the influence of magic on the world."

Halfway through her introduction, Holtzmann's eyes widen. "Mathe...magic," she repeats, dreamily.

"Holtzmann?" Cassie says. There's no reaction from the Ghostbuster. She points down. "You're still holding my hand."

"So I am," Holtzmann says, still not paying the least bit of attention. "How long until the ghosts show up?"

"Twenty-seven—no, twenty-six minutes, fifty-three seconds." A moving target's hard to say. If she'd brought a watch, she could just _show_ the Ghostbuster—Holtzmann—the ETA.

But when Cassie left the Annex, she was expecting to do this alone.

"Twenty-six minutes, good," Holtzmann says. She snaps back to attention. "Please," she says, "tell me absolutely everything about mathemagic."


	2. Chapter 2

Holtzmann sits down against the shelves and pats the floor next to her invitingly. Cassie sits down on the other side of the aisle and tugs her cardigan until it's just right.

"Mathemagic," she says, "is the mathematics of magic."

"Fascinating," Holtzmann says, with a look that Cassie can't interpret as either wholly sincere or completely sarcastic.

"It's a pretty young field, um, actually I invented it." Cassie can't resist a little smirk. "There are a lot of applications but right now I'm studying ley lines. Ley lines are--"

"Lines of power," Holtzmann says, resting her elbow on her knee and her chin on her hand. She's looking dreamy again. "Rowan was charging them up so he could flood New York City with ghosts."

"Right. Unfortunately," Cassie says, "when you closed the vortex, you took away the only place the power had to drain out. It's been washing around New York City ever since, causing problems for _us_ to clean up."

"Huh." Holtzmann doesn't appear perturbed by this news.

"Not that you care." Cassie folds her arms.

"We did wonder why there kept being more ghosts than usual. But we finally caught one and managed to contain it in the lab, so we weren't too upset." She grins fondly.

Cassie looks away. If the Ghostbuster isn't going to be interested, she isn't going to explain herself.

There's a crunch. "Pringle?" Holtzmann asks, holding a canister out to her.

"No thanks. Wait, you shouldn't be _eating_ in a _library_!" She snatches the Pringles away from Holtzmann. The thought does enter her mind that she's being hypocritical, because the Librarians eat meals in the Annex all the time, but that's different. The books are magic there; they can protect themselves.

Holtzmann licks Pringle crumbs off her hands and sighs. "Well, if we don't have any snacks, this is gonna be a boring stakeout."

Cassie doesn't dignify that with a response.

"Hey," Holtzmann says after a few (four point two five) minutes of silence, "is magic basically just weird science? Because ghosts are totally just weird science. Basically what I'm asking is could I engineer magical gadgets and become a wizard."

"Magic is—" Cassie searches for words. "Magic is its own thing. Sometimes it obeys the same kinds of laws science does, and sometimes it really doesn't. And wizards are born with magic, sorry. You could maybe be a mage?"

"Nah," Holtzmann says.

"Are ghosts really science?"

"Close enough for government work," she says, with a sniff. "I built these babies—here, look, see." She unclips a pistol from her pack and passes it over. "There's basically a tiny particle accelerator in the pack"—she jerks a thumb at it—"and then the proton stream is directed through here, right at the ghost. Bam."

Cassie turns the pistol over in her hands. "Proton stream. So are ghosts made of electrons, or—"

"Part electron, part antiproton," Holtzmann says.

"Oh," Cassie breathes, and gestures wide, spreading particles across her vision. One hand is still holding the pistol but it's not relevant, it's gone, it's nothing. "The baryon-antibaryon collision must cause some spillover—but it's not completely annihilated, the electrons intermingle with the protons that are left—"

Holtzmann says, "To harness the ghost." She's nodding.

"—protons, protons, ionic discharge, thunderstorms on a hot summer day, bare feet in the dirt laughing—" Cassie inhales sharply to get air all the way down to the bottom of her lungs and blinks hard to clear her vision. She can taste pineapple, which is strange; it has nothing to do with the thunderstorm, and atomic theory doesn't usually make her think of fruit.

Holtzmann is peering at her. Cassie waits, resigned, to see if Holtzmann is going to pity her or think she's the coolest thing on earth.

"Wow," Holtzmann says, "I thought _I_ was weird."

"Excuse me?" Cassie straightens in a hurry, finds herself still holding Holtzmann's pistol—proton gun—thing, and thrusts it back at her. "You're the one with the Tiny Hadron Collider on your back!"

Holtzmann laughs—at herself, Cassie realizes. "Yeah! I am." She holsters the pistol, checks the time on her watch. "Ghost time," she says with wicked glee, and climbs to her feet. She offers Cassie a hand up like she does this to all the girls. Cassie scorns it, bracing herself on the bookshelves instead.

With a shrug, Holtzmann lets it go. She swaps her glasses for her goggles again, pulls the gloves on, and drops into a crouch. "T-minus two minutes," she says. She scans the area.

Cassie points at where the ghost is going to be. Holtzmann keeps staring around until she happens to glance at Cassie, and then salutes her two-fingered and wheels to face the same way.

They wait. Numbers tick down in Cassie's head. Twenty nineteen eighteen—

"If you got this wrong," Holtzmann says—

"Shh." A blue glow emanates from the books five feet ahead of them. As they watch, it elongates and drips itself out to the floor, rising as it congeals until it's a person-shaped blob.

Cassie's got her stopwatch head running again, whizzing through the hundredths of seconds.

Holtzmann reaches behind her head, pulls out a long-nosed gun, and aims it at the ghost.

"What? No no no! No shooting the ghost!"

"We're called the Ghostbusters," Holtzmann says, still looking at the ghost, a fierce joy in her voice, "what did you think we did, invite them to book clubs?"

"No!" Cassie puts herself between Holtzmann and the ghost. "Look, I have this theory and if my theory is true it'll change everything. I need this one simple little observation and this is my perfect chance to get it. So I just need you to trust me—trust science—and not shoot the ghost."

Holtzmann isn't even _looking_ at her. Cassie stamps her foot. "Holtzmann!"

"Cassie," she says, "you probably want to move."

"And let you shoot it?" Cassie demands.

There's something blue in the corner of her eye—Cassie gasps, and throws herself past Holtzmann. "Okay, okay, okay, I'm moving. But no shooting!" The ghost moves slowly down the aisle toward them, like it's pacing thoughtfully in the library. If this was a library when it was alive, although if it wasn't, how did the ghost end up so high in the air?

One careful step at a time, Holtzmann eases backward, Cassie behind her.

The ghost is coming into clearer focus now: that must mean the power in the ley line is surging. She's got a sensible skirt, a white blouse, and a vest. Her hair is in curls.

"Holtzmann—" The Ghostbuster is the expert on ghosts. This one seems okay, so far, but Cassie's not taking that on faith. "Is she peaceful?"

"I mean, lots of ghosts are, yeah, until they unhinge their jaws and spew ectoplasm all over you, so—" Holtzmann glances delightedly at Cassie: at least one of them is having the time of her life, Cassie thinks, as the numbers run through her head.

The ghost snaps upright like she's seen them, and speeds up.

"Run!" Cassie squeaks. She looks back after three steps and Holtzmann's vanished, somehow, but the ghost is still coming.

"Cassie!" Holtzmann grabs her arm from the side aisle, drags her away. The ghost glides down the row they left, slowing down again now that they're no longer in sight. " _Now_ can I shoot it?" Holtzmann stage-whispers.

"No!" Cassie's still timing, still thinking. "Thirteen more seconds. All I need is thirteen more seconds. If it's here after that, fine. Shoot it."

Holtzmann nods once. She peers through the shelves at the ghost, muttering something. Counting.

Three, two, one—and the ghost fades.

Cassie pumps the air. "Yes! I did it! I figured it out!" Then it hits her _what_ she's figured out. She pulls both arms into her chest. "Oh. Oh, this is not good. Oh this is very not good."

Replacing the gun on her pack, Holtzmann says, "Please tell me the world's about to end." She pushes her goggles up on her forehead.

"New York City's in danger," Cassie says. She starts toward the Library door, then retraces her steps. "And the world, probably. C'mon, come meet the rest of the Librarians." She grabs Holtzmann's hand and drags her away.

**Notes for the Chapter:**

> I only had one semester of advanced quantum in my physics major so my atomic theory's mostly bullshit, sorry.


	3. Chapter 3

They burst through the doors into the Annex. It's now closer to midnight than anything else, but all the Librarians are there—well, no Flynn, but he went off days ago to sign a complicated deal with some mermaids again and nobody expects him to return for at least another week.

But Jenkins is there, looking perplexed, and Eve's at her desk glancing wearily up from paperwork, and Stone and Ezekiel are working on something at the big table that apparently involves a lot of books and swearing.

And then they're all staring at Cassie and Holtzmann instead.

"Hi! Everyone, meet Holtzmann. She's a Ghostbuster. Holtzmann, meet everyone."

Holtzmann, incongruously, sweeps the room a bow.

Jenkins takes two steps toward them, presses his fingers to his lips, and then says, "Cassandra."

"Yes?"

"Why did you bring a Ghostbuster here?" That's Eve, rising from her chair.

"Okay, because," Cassie says, "I ran into her on my mission, because my mission was a ghost, except my mission _wasn't_ a ghost because my mission was the ley lines. They're setting up harmonics—" She hurries to the chalkboard, wipes it clean with big swipes of the eraser, and starts over. The old diagrams were important, but this is more urgent. "When the Ghostbusters closed the portal they created an empty spot at the node, a vacuum. But the power was still in the ley lines so it rushed in to fill that"—she adds chalk arrows—"and then washed back out again." More arrows.

"Like the beach!" Ezekiel says. "I like the beach."

Cassie's withering look intersects with Holtzmann's incredulous one. Cassie rolls her eyes and turns back to the board, hiding a smile. "Right. But the problem is that the power keeps washing back and forth between the nodes, and the ratios and the geometry involved created a feedback loop, so it's just building up and up." She adds an illustrative squiggle.

"The ocean...is building a skyscraper?" Ezekiel asks. He cocks his head to one side.

"It's gonna go boom," Holtzmann says. Cassie looks at her over her shoulder. Holtzmann nods.

"Right," Ezekiel says. "Boom. Boom is bad."

"Boom—explode?" Eve joins Cassandra at the chalkboard, her hands on her well-tailored hips. "Ley lines can explode?"

"The central node can burn out. If it does, best case scenario, the ley lines discharge and take out all the electricity in New York City. Maybe half the eastern seaboard. We spend another six months mopping up the excess magic. Worst case..." Eve was looking like she was about to ask. "The power will flood outward to the next set of nodes, overloading them too, and the next, and the next. And the ley lines will shed power wherever they go, leaving magic in their wake." Cassie puts the chalk down. Takes a steadying breath. "So that's why we need to work with the Ghostbusters. Holtzmann."

"Yep!" Holtzmann raises her hand.

"Your technology. It uses particle interactions to trap the ghosts. I think we can use the same principle to suck in and trap the magic."

Jenkins says, "And then what do we do with it?"

He'd been being awfully quiet. And she knows he's still hesitant about her after the whole Lady in the Lake thing.

Cassie turns to face him. "We get rid of it. Somewhere. Somewhere that more magic can't do any harm."

"I've got a ghost trap that sends everything it catches to Michigan," Holtzmann offers.

Jenkins looks faintly concerned.

"The bottom of the ocean?" Ezekiel suggests.

"Naw, man, there's creepy fishes and things down there," Stone says. "No way."

Cassie clasps her hands behind her back. "I was thinking more like—the center of the sun?"

There's a small silence. Holtzmann's laugh breaks it.

"Far _out_."

"Cassie." Eve lays a hand on her shoulder. "Are you sure this will work?"

Cassie says, "I'm sure we have to try."

#

The Ghostbusters' headquarters is full of bookcases and scientific debris. "Don't touch anything," Holtzmann says, sidling up to Ezekiel with her hands tucked in her pockets.

"Who, me?"

A tall blonde white man gets to his feet from behind a desk. "Hi Holtzmann! You have visitors! They're right there next to you," he says. He beams at them.

"This," Holtzmann says, "is Kevin."

Behind them, Stone and Eve emerge from the Annex doors, which are now the front doors of the Ghostbusters' offices—which are also a firehouse? Cassie does a double take.

"Pretty sweet," Holtzmann says, "right?" She winks at Cassie. "Hey Kevin, where's everyone else?"

"Oh, well, um, Patty's reading, and Erin and Abby—where are Erin and Abby?"

The tall black woman who comes out from behind a bookshelf is holding a fat hardcover book. "Erin and Abby are getting sandwiches for a late-night snack, they'll be back any minute. You are--?"

"New associates of mine," Holtzmann says, with lazy bravado. "This here's Dr. Cillian, and her coworkers Ezekiel and Stone and—sorry, I didn't catch your name."

"Colonel Eve Baird."

"Colonel Baird," Holtzmann repeats to Patty.

"Technically, I don't have a doctorate," Cassie points out. "And Stone does."

"Dr. Stone. Ms. Cillian." Holtzmann gestures to them again. Patty looks bemused.

"Just call me Cassie."

"You're reading _Columns in N_ _ew York Architecture, 1921-1932_? I didn't think that was even out yet!" Stone darts past them all. "His theories on art deco pillars are supposed to be revolutionary."

Patty shrugs. "I've got a cousin works at Barnes & Noble. You want to see the rest of my books?"

Stone nods. They head for the bookcases.

"Touch. Nothing," Holtzmann says to Ezekiel again. "Cassie, my lab's upstairs, you want to go work on how we're going to save the world?"

"We'll be here," Eve says, collaring Ezekiel as he tries to sneak off, "waiting with Kevin."

Holtzmann makes finger guns at Eve. Eve looks past her at Cassie with an expression of _why_.

"Great, good, let's go do science!" Cassie chirps.

Holtzmann says, "My sentiments exactly," and leads the way up the stairs.

There are three chalkboards in Holtzmann's lab, which is good because Cassie should really get all these numbers out of her head onto somewhere other people can see them. Holtzmann inspects the contents of all three, declares one less necessary than the others, and erases it with vigorous wipes of the sleeve.

"Center of the sun," she says then, "center of the sun..." and wanders off, tapping a screwdriver against her hand.

Cassie loses herself in the sheer beauty of the numbers. New York City's ley line and node network is beautiful, really. "Holtz," she calls after ten minutes, "did you take any readings off the ley lines before the vortex went poof?"

"Uh, does the Pope shit in the woods?" Holtzmann asks, appearing from her maze of circuitry. She goes through five pockets before she finds the paper, which she then uncrumples and slams on the table. "Boom."

Cassie doesn't really want to touch that, but she picks it up gingerly and starts copying. The network and the initial power levels combined form an almost numerically perfect system. Combined with the vacuum at the central node, it's just exactly what you'd need to create harmonic resonance.

"Holtz," she yells again, "was that Rowan guy a physics major?"

This time it's five seconds before Holtzmann glides into view, perched on a wheely chair, her goggles fixed firmly over her eyes. "No clue," she says, and shoves off from a table, vanishing again behind her equipment.

"Because these readings are almost too good," Cassie mutters to herself, but shaking her head she finishes transcribing. She stands back when she's done.

Holtzmann says, close behind her, "Oh. Oh, man." There's a pause, presumably while she reads. "Here, come hold this for me."

'This' is something like a bear-trap with green lasers. Holtzmann's opened up its guts, full of wires and a cyclotron like the one in her pack, but she needs Cassie to hold a wire out of the way while she reaches in with pliers to snip another one. Of course, this involves Cassie putting her hand right in through the mouth of the trap.

"Don't worry, it won't close on you. Probably." She's trying to look serious, but a giggle escapes.

Cassie shoots her a dubious look. "Holtzmann, if we're going to work together—"

Holtzmann flips the lenses of her goggles up—Cassie is momentarily distracted by the fact that this defeats the entire purpose of goggles—and stares at Cassie for several seconds. Just as Cassie's getting uncomfortable, she shifts her gaze to somewhere behind Cassie's left shoulder. "Life is...a series of risks and I take more of them than most because the stuff I work with levels cities," she says rapidly, "and so I'm always clear what risks I take and that's what I want you to know too." She makes eye contact with Cassie briefly, looks away again, and picks up her pliers.

"Thank you?" Cassie says. "I think." She's not sure if that was Holtzmann's idea of being reassuring.

"I mean there's like a five percent chance," Holtzmann says, gesturing with the pliers. It's kind of comforting, until she adds, "But it'd be pretty funny if it did, huh."

"Please tell me you are not going to send my arm to Michigan as a joke," Cassie says.

Holtzmann sighs. "All right," she says, like it's a favor.

Cassie eyes Holtzmann narrowly and puts her hand down through the trap to hold the wire.

Holtzmann does what she has to do in fifteen seconds flat. She lifts a tiny piece of computer chip out, holding it carefully level with the pliers. "Okay."

Cassie tries to look like she isn't yanking her hand back before the trap could possibly slam shut on it. She's pretty sure she fails. Fortunately, Holtzmann's wandered off, pushing her goggles up and holding a magnifying glass up to one eye so she can peer at the chip she removed from the trap.

"Yes," she says, "yeah, this is the one. Mm." She drops the chip into a petri dish, and then tips her head, listening. "Erin and Abby are back!"

They come down the stairs together. Two white women, one skinnier than the other, stand inside the front door holding sandwich bags. Eve's fallen asleep on Ezekiel, who looks like he's trying to figure out how to escape without waking her up. Kevin is gone. Patty and Stone are sitting by a bookcase, piles of books next to and between them. From the sounds of it, they're having an argument about architectural details.

The skinnier woman is staring at Stone with undisguised longing. The other one's frowning at Eve and Ezekiel. "Were they here when we left?" she asks her companion, and then notices her distraction. "Hey. Erin!"

"Huh, what?" Erin says, surfacing, and then glances at Stone again. She clearly can't keep her eyes off him.

Neither of them has apparently seen Holtzmann or Cassie yet. Erin's the professorial type that Cassie always thought her own future self would look like; the other one—Abby?—is a sloppier dresser, but also looks nicely put together for the time of night, which is probably about one in the morning.

Cassie edges closer to Holtzmann. "Your coworker is staring at my coworker," she whispers.

Holtzmann slings an arm over her shoulders. "Ah, Cassie," she says in sententious tones. "That is the spectacle of heterosexuality, which higher beings like yourself and me are not troubled with."

Cassie lets herself lean for one moment against her. She's so tired.

"Aw, jeez, not again," Abby says. She's looking at them. "Look, whoever you are, that's great, but we don't need any fangirls in here." She waves her sandwich bag in what's probably meant to be a threatening manner.

Holtzmann says with great dignity, "Cassandra Cillian deals with mathemagic."

"Mathe-who-now?" Abby says.

"We're saving the world," Holtzmann adds brightly. "Wanna help?"


	4. Chapter 4

Halfway through Holtzmann's explanation, Abby sits down. "Lemme get this straight," she says. "You two are going to save the world by sending a bunch of magic into the sun?"

Holtzmann looks at Cassie, who nods.

Erin wanders faux-casually toward the bookcase corner. "Patty, uh, we got you a sandwich."

Abby gestures incomprehensibly. "Have you even _thought_ about what that'll do to the ionosphere?"

Cassie looks at Holtzmann. Holtzmann looks at Cassie.

"Jeez," Abby says again, and takes her sandwich out of the bag. "I'm gonna eat this, and then I'm gonna come check all your numbers, okay? No exploding the atmosphere until I get up there."

"Yes ma'am," Holtzmann says.

"Also, you, what are you doing here." Abby points her sandwich at Ezekiel, who has finally managed to tip Eve onto the chair instead of his shoulder.

Ezekiel turns. "Who, me?"

"He works with me," Cassie says. "We're all Librarians. Um. Magic librarians."

"Right," Ezekiel says, "like she said. Magic librarians. Except her." He jerks his thumb at the slumbering Eve. "She's our Guardian."

On anyone else, this happy collaborative spirit would be reassuring. On Ezekiel, it just makes Cassie start looking around for whatever he's about to steal.

Abby snorts. "Sounds more like someone needs to guard everything else from you. Didn't even think about the effects on the ionosphere..." She shakes her head and takes a bite of sandwich.

"Okay, well, we're gonna go keep working until you're done," Holtzmann says, her frenetic energy returning. It's contagious: Cassie follows her, despite the yawn that threatens to crack her jaw.

Upstairs, Holtzmann makes a beeline for the petri dish with her chip. "I have to rejigger the coordinates and figure out a siphon system. I assume we don't want to drain the ley lines completely?"

"Definitely not." Cassie settles in to work on establishing the precise amount of magic to remove, and which points in the network would be the best to draw it from. It takes her another chalkboard's worth of space, which Holtzmann shrugs one-shouldered about and lets go.

When she's covered the chalkboard, there are still a few details she's unclear on. If she just—

She takes a step back, opens her arms, and lets the math in. It twinkles around her, nodes in New York's ley line network glittering like stars. Stars, constellations, Orion, Leo, Ursa Major... the scent of ozone, product of magical discharge or the interaction of sunlight with the atmosphere, sharp in her nose. The smell of wet dirt after rain, the green of leaves gleaming damply, the green of grass as she lies in it as she lies in it as she lies in it thinking about what the doctors told her.

"Hey." Holtzmann's voice is low and insistent and very close by. "Cass. Hey." Her hands are on Cassie's elbows. She's steering Cassie to a chair. An armchair, by the feel of it. Cassie sits. She waits again for recriminations, demands for an explanation, pity.

"Did you get the answer?" Holtzmann says instead.

It's shining in her head. "Yes," Cassie whispers.

"Good," Holtzmann says. She pats Cassie's shoulder and stands up with a creak of her boots. Cassie closes her eyes. She'll get up in just a moment and write the answers down, but it's so nice to sit here—there's room enough to pull her legs up, curl against the upholstered arm of the chair...

Cassie wakes to bright sunlight. She's sore all over from sleeping in a chair, but her head is remarkably clear. She sits up, and a brown leather coat slides off her. Cassie catches it before it falls to the floor.

Holtzmann's maze of equipment, tables, and experiments are all she can see. Cassie folds the coat, puts it on the chair, and gets up. She wanders for a while, trying to figure out what everything is. Some she recognizes, some she can figure out from first principles, and some stump her entirely. She makes a list of the third category in her head so that she can ask Holtzmann later.

When she's seen everything and she's pretty sure Holtzmann's not up here—unless, of course, she's hiding, which isn't out of the question—Cassie goes downstairs. Kevin's back at his desk, Ezekiel and Erin are gone, and Eve and Abby are talking at a table that looks like it was once a booth at a Chinese restaurant. Stone and Patty are reading, the remains of a take-out breakfast near them. Stone's got the book that Patty was holding the night before. Patty is carefully holding a manuscript that Cassie recognizes from the Annex reading room table. They both look wholly absorbed.

At the other end of the room, there's a little galley kitchen where Holtzmann is pouring coffee into a succession of mugs. She's wearing high-waisted green trousers, a white collared shirt, and a tan vest. Her hair is somehow still perfect. As she turns, four mugs perched precariously between her hands, Cassie sees she's got a multicolored silk scarf tied loosely like a tie around her neck.

Cassie smooths her skirt out, which is wrinkled from sleeping, and wishes for a shower and a change of clothes.

Holtzmann sees her and brightens. "Good!" She carries the mugs toward the booth, managing to communicate via shoulder wiggle and head motion that Cassie's to join the group.

Cassie slides in beside Eve and takes a mug of coffee. The mug has a cheerful biohazard symbol. Eve's, she notes, says in bold letters "Particle physics gives me a hadron." Eve gives the mug a pained look, but she drinks the coffee.

"We think—we _think_ we managed to figure out how to not blow the ionosphere to bits," Abby says. She pushes a paper toward Cassie. "Here, take a look-see."

Cassie reads. Holtzmann's fidgeting under the table, her foot tapping, which is distracting, but Cassie gets the gist of it. "If we combine that with some classic protective runes, I don't see why it shouldn't work."

"Protective runes," Holtzmann says. " _Awesome_."

Eve asks, "So what's the timeline?"

"As soon as we can." Cassie glances between all of their faces. Eve's intent, Abby's serious, Holtzmann is stifling something. "I figured out last night, if we put siphons in five places it should help balance the energy in the ley lines while we're taking out the worst of the overload." She draws them out on the table as if it's a map. Holtzmann stares unblinking at the table, like she can really see all of New York City laid out. "If we can reduce the power in the lines by, say, thirty percent, that should fix the immediate problem."

"All right, well, let me just—" Holtzmann digs in the pockets of her trousers. She first takes out glasses, which she places delicately on the bridge of her nose. Then, from her other pocket, she pulls a six-inch-long thing that's a cross between a whisk and a funnel. "The tines here collect energy off of the ley line using the same technology as our proton guns. It connects up to the pack to use the cyclotron power, but the ley line power that's collected has to go somewhere, so I've added a second connection directly to the ghost trap." She grins. "Then we just need the uplink to the coordinates and something to direct the power." Jumping up, she runs to a pile of what Cassie had thought were broken TV antennas. "Bam. If we set these to the right frequency, the power should bypass the ionosphere completely."

"Yeah, which I calculated, you're welcome very much for not destroying the planet you're trying to save," Abby adds. She gulps her coffee.

Eve raises her mug. "I for one appreciate that."

" _Thank_ you. I like you. I like her," Abby tells Holtzmann.

"I like you, Abby!" Kevin yells from his desk.

Abby sighs. "Thanks, Kevin!" she shouts back. "All right, let's get to work."


	5. Chapter 5

Cassie and Holtzmann drag all the equipment upstairs. "Doesn't this place have an elevator?" Cassie says when she stops to pant.

"Nope!" Holtzmann's voice echoes down to her, entirely too cheerful.

Holtzmann dives into one of her piles and digs up an electrical engraving pen. She sets Cassie up with it at a workbench that's only half covered in debris and partially-built devices, frowns at her, and then leaves. Darting back a moment later, Holtzmann dumps a folded leather apron on Cassie's lap and puts a pair of perfectly normal, clear lab goggles on the table. So she does own _some_ ordinary goggles, even if she never uses them.

Cassie puts on the protective gear and gets to work.

The pen is hard to control, and the runes have to be just right. Cassie uses both hands to guide it along the curves of each shape, pausing every time she has to push her hair out of her face. She's sweaty by the time she's finished.

When she puts the pen down, wrists aching, she expects Holtzmann to materialize at her side. But she doesn't: in fact, the lab is silent.

"Holtzmann!" Cassie calls, feeling a little silly.

There are a few muffled clanks and crashes. Twenty seconds later, Holtzmann emerges from her maze.

"Yeah? Oh—nice!" She hones in on Cassie's handiwork, muttering to herself about the Golden Ratio and hyperelliptic curves.

Cassie props her sore arms on the worktop, feeling pleased with herself.

Holtzmann turns to her. "They're magnificent," she says, the most sincere Cassie's heard her. Then, as happens so often, her attention is caught by something else: only this time it seems to be Cassie's face. "You've got some grease, there." She taps her own cheekbone.

Cassie groans. It must've been from getting her hair out of her eyes. She scrubs at the place with the back of her hand. "There?"

"Not quite." Holtzmann hesitates, looking—shy? She reaches toward Cassie, but slowly; Cassie could lean away if she wanted to. Cassie holds still. Holtzmann's thumb brushes her cheekbone. "There." She squints. "Well. Mostly."

Her hand is gone, but Cassie can still feel it, her engineer's calluses, the gentle touch. Cassie is angled toward her anyway, and Holtzmann's standing right next to her stool. It just makes sense to lean over and down, and kiss her.

Cassie's kissed people before. She's kissed girls before. But here she is in someone else's lab, surrounded by the tangible artifacts of that someone's love for the infinite possibilities of the universe and her desire to understand them. Here she is _with_ that someone—someone whose disregard for safety precautions is frankly troubling but whose reasons for that disregard make all too much sense—with that someone's hands in her hair, with her own hands on that someone's neck despite the grease that's probably staining the collar of her shirt, and Cassie can't seem to stop kissing her.

They break apart, and Cassie winces. She did leave grease on Holtzmann's shirt, just little smudges on the inside of her collar, and on her neck.

Holtzmann traces the shape of Cassie's face. "Hmm," she says, seriously.

"We should go save the world." Cassie wants to put her fingers in Holtzmann's hair and take out all the dozens of pins that are undoubtedly keeping it up. She wants to kiss Holtzmann's slowly growing self-satisfied look right off her face. She wants to solve the mysteries of the cosmos with her.

"Nah," Holtzmann says, stretching the word out, and winks at her. She offers her hand.

Cassie takes it to jump down from the stool. Without exchanging a word, they start loading up the equipment to take it back to the others.


	6. Chapter 6

Patty and Abby sling their packs on without hesitation. Stone eyes the equipment dubiously, but he takes a proton pack from Holtzmann and then almost drops it. Swearing, he adjusts his grip and puts it on.

Eve, settling hers in place, says, "All right, Cassie. What's the plan?"

Cassie shows them. By the time they get out to the curb, Holtzmann's waiting in the car.

"You drive...a hearse," Eve says.

"They said we had to be inconspicuous," Holtzmann drawls. "C'mon, get in."

They all pile in. Cassie's squished in the back between Stone, Abby, and Eve.

Turning, Patty says from the front seat, "We borrowed the first one from my uncle but it got, uh, sucked into the ghost vortex, so the city bought us a new one." She pauses, considers. "Bought us two. We gave one to my uncle."

Stone says, "So that's why the license plate says—"

"Ecto-two?" Patty asks. "Yeah."

Holtzmann drives the way she does everything else: quickly and with enthusiasm. Cassie holds onto her seat and tries not to squeak. They drop off Eve, Abby, Patty, and Stone in succession that would've been quicker if not for New York traffic. Everyone gets a walkie-talkie so that they can coordinate.

Finally, Holtzmann pulls the Ecto-2 up outside the Mercado Hotel. "Here you go."

Cassie thanks her and scrambles out.

"Oh, hey, I made you something," Holtzmann says before she can close the door. She tosses it. Cassie almost fumbles the catch, but she makes it. It looks kind of like a handheld radar receiver, but the screen is a pattern of lines as though it's an Etch-a-Sketch. Some pieces of the lines are brighter, some darker.

"Holtz," she says, even though she thinks she knows, "what is this?"

"It's supposed to detect ley lines," Holtzmann says, "but I'm not sure I calibrated the—anyway, does that look right?"

The screen blinks and updates itself, the pattern of bright and dark shifting. It tracks exactly with the numbers in Cassie's head.

Cassie nods.

"Good," Holtzmann says, and drives away.

Cassie wanders a few doors down, hoping it looks she's waiting for someone, and watches the pattern of energy move through the ley lines. It's just as she calculated it. In twenty-five seconds, it will move— _there_. She raises her walkie-talkie. "Holtzmann, are you in position?"

"In position, over," Holtzmann's voice crackles back.

"Abby? Eve? Patty? Stone?"

One by one, they confirm.

Magic swells in the ley lines. Cassie counts silently, math and geometry blossoming in her head. She presses the talk button down. "Now."

Dark spots bloom against the map. Darker, darker, and then they bounce back a little—Abby's first, then Stone's, and then Patty's and Eve's and Holtzmann's. Cassie nods, half in a trance as the numbers dance through her head and across her screen. The network is trying to balance out. The Ghostbusters and Librarians are still draining it, though, and the brightness fades again.

Just a little more, and—"Stop," Cassie says.

There's a little flash at each of the five spots, a power surge, that Cassie wonders if any of them can feel. But the ley lines are settling again—a little brighter, a little darker, the change a bit smaller every time until it's imperceptible to Cassie's eye.

She lets out her breath. She'll have to observe the network for a few days, but life in New York City should be back to normal.

She presses 'talk'. "We did it."

"All right!" Abby crows, her voice a muzz of static.

Stone says, "Not bad for a day's work."

Holtzmann whoops, the sound too big for the walkie-talkie it comes out of.

Cassie beams, listening in as everyone celebrates. She'd never expected to belong anywhere like she does with the Librarians. Now, it seems, she has even more than that.

The walkie-talkies gradually quiet. Then Cassie's crackles to life again in her hand.

"Now that the world is saved, or whatever, can we go back to the part where magic is real?" Abby asks.

The Ecto-2 pulls up at the curb, blatantly on the wrong side of the street and, as a bonus, ignoring the orange cones that indicate that this is a construction zone.

"Hey," Holtzmann says, one arm resting on the open window. "What's a girl like you doing in a place like this?"

"Oh, you know," Cassie says, with a flip of her hand. "Saving the world." She leans down, enjoying the slight surprise in Holtzmann's eyes and the fact that Holtzmann doesn't move an inch, and kisses her.

When they part, Holtzmann looks like she's going to say something, but Cassie beats her to it. "By the way, did I mention earlier that I'm sort of Merlin?" She summons her blue spell-light, flicking it casually into existence.

Holtzmann looks fascinated and also turned on, which is what Cassie was hoping for. "No," she says. "I don't think you did."

Cassie saunters around to the passenger side and slides in. Holtzmann still has an astonished expression. Cassie isn't sure she should be enjoying it this much, but she really is. "Are we making everyone else take the subway?"

"Hell yes," Holtzmann says, and stomps on the gas.

Cassie fastens her seatbelt after five seconds of heart-stopping speed, puts her head out the window, and laughs all the way back to the firehouse.

**Notes for the Chapter:**

> There's going to be a last chapter/epilogue, so stay tuned!


	7. Chapter 7

At the firehouse doors Cassie stops and looks up. "Holtzmann," she says.

"Yup?" Holtzmann swings around, and then follows Cassie's pointing finger. "Huh." She pulls her glasses down her nose.

The sky is a nice rosy pink color. Cassie has spent a lot of time at weird hours lately but it is definitely the middle of the afternoon right now—not remotely near sunset.

"Back-spill radiation?" Cassie muses aloud. "Or the frequencies were a little off."

"If we'd destroyed the ionosphere we'd be dead by now," Holtzmann says, "so I'm sure it's fine."

Cassie casts a doubtful look upward, but follows Holtzmann in. "We can ask Abby when she gets back." She bumps into Holtzmann, who's stopped just inside the doors.

"He touched something," Holtzmann says, and gallops upstairs.

Cassie doesn't need to ask who. She just runs after her, reaching the third-floor doorway just as Holtzmann begins to swear. The word 'idiot' features prominently.

Cassie's never been up here before, but it's obvious that something is missing. There are two work areas, Abby's and Erin's probably, and though neither of them are as messy as Holtzmann, the large rectangular clear space by one wall is obviously not normal.

Holtzmann pulls at her hair, dislodging several pins. "Your coworker _stole_ our _ghost_."

There is nothing Cassie can say to that, because it's indisputably what happened.

"Technically, as a magical entity, the ghost belongs in the Library," Ezekiel says behind Cassie.

Holtzmann makes an inarticulate noise.

"Okay," Cassie says hastily, "let's just take a minute. Ezekiel, good job, you stole a ghost. I bet you're the first person to ever steal a ghost. So maybe you could take the win and..." She gestures. "Bring the ghost back?"

"If I bring it back it's not stealing."

Cassie looks at him. He shoves his hands in his pockets.

"You don't know how," Cassie says, "do you."

Ezekiel busily inspects the ceiling.

Cassie sighs. "Holtzmann, if you want a new ghost, I will help murder him." There's no answer, so Cassie glances at her.

Holtzmann's gone distant again. "It's an interesting challenge," she says. She's probably not talking about murdering Ezekiel. "I lost my notes in the last explosion so I'll have to work backward—I could improve—oh. Oh! That would work _much_ better. Why didn't I think of that before?" She slaps herself in the forehead and strides toward the stairs. Cassie and Ezekiel get out of her way.

Three steps down, Holtzmann twists to look back. "Erin's gonna kill you, though. She loved that ghost. She spent hours right up next to it even though I hadn't gotten the calibration right and the ghost leaked out a little bit so you could hear its thoughts." She shudders. "That ghost loved boiled eel."

Half a flight later, Holtzmann calls, "Abby's going to be pissed too. She said something before about this being the culmination of her life's work?"

Holtzmann's entirely out of sight when she shouts up, "Oh hey, they're here!"

Ezekiel groans. "Cassie," he says. "Distract them so I can sneak out."

Cassie says, "Nope." She heads down the stairs after Holtzmann, peeks into the second floor long enough to see that she's rooting through a box of spare parts—tossing the rejected ones, or maybe the ones she wants, away with no regard for where they land—and then keeps going to the first floor, where loud music has started playing.

Abby's grooving to the music. Stone looks belligerent, but his toe is tapping. Eve has apparently decided to go with it and is dancing with Patty.

"Cool, a dance party!" Kevin says, coming into the firehouse, and joins in.

Cassie ducks around everyone, opens the firehouse door the correct way to make it the entrance to the Annex, and goes through. If Ezekiel gets caught, it's his own problem. She is going to take a goddamn shower.

#

Freshly scrubbed, in a clean skirt decorated with mathematical symbols and a light blue blouse, Cassie steps back into the firehouse. The music is still on, but turned down lower. Patty, Eve, and Abby are sitting in the booth drinking beer. Kevin's boogying alone in a corner. Stone and Erin are, improbably, slow-dancing.

Cassie refuses the offer of a beer and wanders up the stairs.

The box of parts is gone, and Holtzmann's nowhere to be seen. Cassie follows the trail of discarded objects to the back of the lab, where there's a nearly-empty workbench that Holtzmann definitely cleared by putting all the piles onto the floor.

"So exactly how guilty does Ezekiel feel?" Holtzmann asks without looking up. She carefully snips a wire. "Because some of those parts were actually kinda hard to find in dumpsters."

"Ezekiel doesn't really do guilt." Cassie watches her work for a while. "I'll be downstairs," she says, resting her hand on Holtzmann's shoulder.

Holtzmann drops her pliers, reaches up, and drags Cassie down for an intense kiss. Her goggles get in the way, but it works out all right. "Okay," she says when they part, and picks up her pliers.

Cassie giggles, her knees a little weak, and leaves her to it.

Hours later, she's had a couple of drinks. Eve and Patty are comparing notes on their headstrong, reckless colleagues. Abby has attempted three times to explain why the sky turned pink, but she's tipsy and keeps swapping the beginnings of her words, so Cassie still isn't sure what happened. Stone is halfway through an involved description of the dissertation he wrote for his second PhD, and part of Erin's interest might even genuinely be for the topic.

Holtzmann comes down the stairs one at a time, hands in her trouser pockets. She quirks her eyebrows at Cassie.

"Holtzy," Patty says, "you want a beer?"

"Nah."

Patty shrugs and goes back to detailing a Ghostbusters exploit for Eve.

"You want a frilly drink?" Cassie asks. "Because we can make those. Erin showed me all the stuff." There's a surprisingly well-stocked cabinet in the galley kitchen. The other cupboards mostly hold ramen, coffee, and Red Bull.

Holtzmann shakes her head.

Abby looks between them. "Oh," she says. "Ohhhh." She tries to point at both of them, but she's holding a beer in one hand and gets confused. "You two. The you of two."

Cassie can't help a smile at Holtzmann, who grins bashfully back. "You want to get out of here?" Cassie says. She tries to stand, but overbalances and thumps down on her butt. "Ouch."

Holtzmann gives her a hand up.

"Hmm," Cassie says, leaning against Holtzmann and wrapping an arm around her for extra support. "Let's go...somewhere...ooh, I know." She waves at Eve, who isn't paying attention, and tows Holtzmann to the firehouse's doors. The Annex's doors.

"See," Cassie says, "from here we can go anywhere." Spinning the globe around, she tries to find the right spot. She goes past it twice, but gets it right the third time. "There. But we'll need warm coats." Fortunately, Eve keeps a nearby closet well-stocked with gear the Librarians might need on any venture.

Properly geared-up, they step out again into somewhere dark and cold. A low bunker huddles against the ground behind them. They got there just in time: Northern Lights are just starting.

Cassie tucks herself against Holtzmann's side and sighs happily. The aurora borealis spill across the sky, all kinds of improbable colors flitting through the bands and streamers of light.

"The last time I was here, Eve had to become Santa Claus and deliver joy across the world," she says, her words making puffs of steam in the cold air.

Holtzmann wraps an arm around Cassie. "I _knew_ Santa Claus was real."

"Me too," Cassie confides.

"I made a trap for him when I was a kid, but I got the atomic weight of cesium wrong, so it went off before I even got into bed." She pauses. "By 'went off' I mean 'exploded.'"

Most things do where Holtzmann is concerned.

The colors dance above them. There are shapes in them: buildings, towers, a garden, a flock of dragons flying. Cassie doesn't think she's imagining them.

"We sent all that power out..." Cassie thinks out loud. "If a little burned off in the atmosphere, it might thin the walls between dimensions."

"Like to the ghosts' world?" Holtzmann doesn't sound ruffled. Cassie is weirdly calm herself. Jenkins would definitely freak out if he saw it. She hopes he's safely indoors somewhere with a nice cup of tea.

"There are lots of dimensions. Once we all got trapped in different ones—I commanded dragons in mine." She knows she's not supposed to enjoy thinking about it, but she does. Lamia was good in that one, or Cassie was evil, or they were both somewhere in the middle. They'd been lovers for years. Cassie daydreamed about that dimension for weeks after they sorted the universe out.

But now, she isn't sure but that this dimension might be the best one of all.

With a last look at the aurora, Cassie pulls away from Holtzmann. "Brr," she says. Holtzmann looks cold, even if she hasn't said anything—which might itself be telling, now that she thinks about it. "Let's get inside."

The survey station looks like no one's been here since the Librarians' visit. The generator roars into life when Cassie flips the switch, and the blankets are right where they left them on the beds, covered in a thin layer of dust. Cassie pounces on them to shake them out.

Holtzmann's standing just inside the door, looking around. She hasn't even taken her gloves off or unwound her scarf.

"Unless...you'd rather go back," Cassie says, hesitant.

Holtzmann laughs. "Erin is definitely gonna find out that Ezekiel stole our ghost tonight and I so do not want to be around for that. I mean, I kind of do, but mostly I don't." She unzips her coat. "Nah. I was just wondering why we don't have a magic door that takes us places."

Feeling a lot more certain of herself, Cassie says, "I've done some experiments on the door and I have a working theory about how it—"

Holtzmann crosses the space between them in four steps and kisses her, stifling the rest of Cassie's sentence.

Cassie fully intends to protest, but they're alone together in the middle of nowhere and the world is safe, for now, and they have the rest of their lives—however long that is, with Cassie's brain grape and Holtzmann's penchant for blowing shit up—to science the fuck out of some magic. So she makes a mental note to explain it later, pulls Holtzmann closer by the lapels of her coat, and kisses her fiercely back.


End file.
